The objective of undertaking this project was to develop a system, employing the technique of reverse plaque assay that could be used to study spontaneous and induced mutations in mammals using readily available single cells; namely, red blood cells. Antibodies against some of the mouse hemoglobin variants have been raised. A unique plaque assay for mouse red blood cells has been developed using these antibodies. Potential use of this method for detection of mutation in mouse hemoglobulins is being worked out.